The invention relates to an apparatus comprising a display device having a flat display, provided with means for visualizing images in two planes located on opposite sides of the display. The invention also relates to a display device for such an apparatus.
Examples of such a display device are TFT LCDs or AM LCDs which are used in laptop computers and in organizers, but they also find an increasingly wider application in GSM telephones based on both passive and active drive. Instead of LCDs, display devices based on other effects such as, for example, electroluminescence may also be used.
Electronic apparatus in which the information can be visualized on two sides of the display is increasingly being used, not only in said laptop computers and organizers but also in, for example, cash registers.
In the known apparatuses, two different displays are generally used, one for each of the two viewing sides. It will be evident that this has a considerable cost-increasing effect, even if only two substrates are used for realizing the two displays, as is shown in GB 2,305,232.
It is an object of the present invention to provide a solution by providing the display device with sub-pixels associated with pixels which are visible on both sides of the display, which sub-pixels are provided with electrodes on at least a first substrate, each electrode comprising a transparent and a reflective sub-electrode.
The sub-pixels will usually coincide with pixels although the surface of a pixel intended (and also observed) as a single pixel on one side may comprise a plurality of sub-pixels as observed from the other side.
In a first embodiment, which may be based on light-modulating effects such as LCD effects as well as on emissive effects such as (organic) LEDs, the first substrate and the second substrate are provided with electrodes each comprising a transparent and a reflective sub-electrode, in which, viewed transversely to the substrates, the transparent and the reflective sub-electrode are substantially complementary with respect to each other.
By driving, during viewing from one side, the reflective sub-electrodes with or without simultaneous illumination with a lamp functioning as a frontlight in the embodiment based on light-modulating effects, the display device is used as a reflective display device in one mode.
When viewing from the other side, the transmissive sub-electrodes are driven, in which the same lamp now functions as a backlight.
Another embodiment, based on emissive effects, comprises a light-emitting material between two transparent substrates in which again, viewed transversely to the substrates, the transparent and the reflective sub-electrode are substantially complementary with respect to each other.
By driving, during viewing from one side, the appropriate sub-pixels, light is emitted in the display device in one mode via transmissive sub-electrodes, while light is emitted in the other mode via transmissive sub-electrodes which are complementary therewith on the other side.
These and other aspects of the invention are apparent from and will be elucidated, by way of non-limitative example, with reference to the embodiment(s) described hereinafter.